Why does it work from my office but not from Docker?

Docker’s default bridge network has no IPv6. The pooler host resolves over IPv4 from anywhere.

Is the pooler slower?

Negligibly for application traffic. Session mode behaves like a direct connection; transaction mode cannot hold session state, so prepared statements and advisory locks need session mode.

Does the password change?

No. The username changes to postgres. ; the password is the same database password.

Can I add IPv6 instead?

Yes on your own servers; on a laptop or a managed runtime it is often not yours to change. The pooler is the dependable route.

Fix · Infrastructure

Postgres: "could not translate host name" on a Supabase direct connection.

psql: error: could not translate host name "db.<project>.supabase.co" to address, from a laptop, a container or a cloud runtime that worked elsewhere.

Cause.

Supabase direct database hosts resolve to IPv6 addresses only. A network, a Docker bridge or a cloud runtime without IPv6 cannot resolve or reach them. The connection pooler host resolves over IPv4.

Fix.

01	Switch the host to the pooler: aws-<n>-<region>.pooler.supabase.com, port 5432 for a session connection or 6543 for transaction mode.
02	Change the username to the project-scoped form: postgres.<project-ref>.
03	Keep the same password; the pooler authenticates against the same roles.
04	For migrations and long transactions use the session port; for serverless runtimes use the transaction port.
05	Record the pooler connection string in the runbook so the next person does not rediscover this.

How the build avoids it.

KYN runbooks carry the pooler string for every Supabase project and the migrations run through it; direct hosts are used only from networks known to have IPv6.

Postgres integration →Infrastructure →Every infrastructure article →

Checked 13 October 2026 against a live build. Vendors change behaviour; if a step no longer matches, tell us and the page changes.

Questions operators ask

Why does it work from my office but not from Docker?: Docker’s default bridge network has no IPv6. The pooler host resolves over IPv4 from anywhere.
Is the pooler slower?: Negligibly for application traffic. Session mode behaves like a direct connection; transaction mode cannot hold session state, so prepared statements and advisory locks need session mode.
Does the password change?: No. The username changes to postgres.<project-ref>; the password is the same database password.
Can I add IPv6 instead?: Yes on your own servers; on a laptop or a managed runtime it is often not yours to change. The pooler is the dependable route.